Colt Defense CM556-16-M5S: The Colt M5 Carbine features a completely redesigned lower receiver and upper receiver with full ambidextrous controls and an enhanced upper receiver rail design which ensures extreme rigidity. - With maximum performance and ergonomics at the forefront of the design consideration the Colt M5 Carbine utilizes a proven carbine length gas system with Colt's new purposedesigned free float rail and upper receiver system. - The Colt M5 Carbine is truly the next generation in a long legacy of Colt high performance rifles